Jet atomization and cavitation induced by interactions between focused ultrasound and a water surface

Abstract

Atomization of a jet produced by the interaction of 1 MHz focused ultrasound with a water surface was investigated using high-speed photography. Viewing various aspects of jet behavior, threshold conditions were obtained necessary for water surface elevation and jet breakup, including drop separation and spray formation. In addition, the position of drop atomization, where a single drop separates from the tip of a jet without spraying, showed good correlation with the jet Weber number. For a set of specified conditions, multiple beaded water masses were formed, moving upwards to produce a vigorous jet. Cavitation phenomena occurred near the center of the primary drop-shaped water mass produced at the leading part of the jet; this was accompanied by fine droplets at the neck between the primary and secondary drop-shaped water masses, due to the collapse of capillary waves.

Periodicity in ultrasonic atomization involving beads-fountain oscillations and mist generation: Effects of driving frequency

“…The occurrence of oscillation mode of the beads was confirmed several times before/after the droplets bursting or mist spreading, which is noted to be observed out of a bead (at a time) along the fountain rather than one at its top (cf. [38] , [37] ).

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“…Cavitation bubbles, if present, could contribute to such selective separation from a multicomponent system like alcohol–water solutions—in symbiosis with capillary instabilities—associated with UsA ( e.g. , [33] ); other supportive references of this conjunction hypothesis include Boguslavskii and Eknadiosyants [34] , Rozenberg [35] , Barreras et al [36] , Simon et al [16] , [37] , Tomita [38] , and Zhang et al [39] .…”

“…Some visual evidence has been reported in regard to the formation of μm-size droplets—pinched off under parametric decay instability of capillary waves of microscale [7] —stemming from interfacial oscillations occurring along a perturbed protrusion or a conical fountain/column of solution [36] , [41] . There has been, however, little direct (visual) evidence that links the mist formation to the occurrence/prevalence of cavitating bubbles within the liquid fountain [42] , [38] , [37] . Firstly, the presence of cavitation bubbles under sonication—or “active” bubbles of size usually too small to be individually imaged—have been mostly inferred visually from a long-time exposure of the sono[chemical] luminescence, i.e.…”

“…The same line of study has been conducted using a different type of transducer with focused ultrasound, often employed in medical applications [38] , [16] , [37] . Tomita [38] investigated, through high-speed (as high as 50,000-fps) photography, atomization of a liquid jet generated by interactions of 1-MHz focused ultrasound with a water surface. He identified the threshold conditions for surface elevation and jet breakup associated with drop separation and spray formation.…”

A fifth-order high-resolution shock-capturing scheme based on modified weighted essentially non-oscillatory method and boundary variation diminishing framework for compressible flows and compressible two-phase flows

“…Compressible two-phase flows are widely found in a wide spectrum of phenomena, e.g. cavitation [13,26,38,35,57,40,7,4]. Driven by the great demand of these engineering applications, the study and understanding of the physics behind compressible fluid dynamics is crucial.…”